The Missouri Legislature passed a bill Wednesday that would require voters to show photo identification at the polls, sending the proposal to Democratic Gov. Jay Nixon with enough support to overcome a possible veto.

If the bill makes it past Nixon, it would only go into effect if voters approve a separate proposal to amend the state constitution.

Republicans have tried for a decade to require a photo ID to vote in Missouri - the state Supreme Court struck down such a proposal in 2006, and Nixon vetoed another bill in 2011. This session, faced with attempts by Senate Democrats to block the legislation, GOP lawmakers agreed to pare back the proposal.

Under the bill, people without photo identification could still cast a ballot after signing a statement saying, under penalty of perjury, they don't have the required identification and can show some other form of identifying document, such as a utility bill or paycheck. The bill also calls for the state to cover the cost of IDs for voters who do not have them.

This is "the most generous photo ID bill that this country has seen," Rep. Shamed Dogan, a Republican from Ballwin, said before the legislation passed 112-38.

Because the Missouri supreme court has ruled against such measures in the past, lawmakers are also asking voters to change the constitution to give the Legislature the power to require a photo ID to vote. The proposed constitutional amendment still needs another vote in the Senate and House before reaching the ballot. It would not need the governor's approval.

Democrats, who say voter impersonation fraud is virtually nonexistent and that requiring a photo ID would disenfranchise some voters, warned that changing the constitution could invite more restrictive measures in the future.

"House Democrats have absolutely no confidence that this version of photo ID will long remain law if enacted," Rep. Gail McCann Beatty, the assistant minority floor leader, said in a statement. "It is virtually guaranteed that next year the Republican legislative majority will swiftly replace this so-called compromise with the strict legislation that they have long desired."

The voting rights granted under the Missouri Constitution are stronger than most other states, said Rep. Stacey Newman, a St. Louis Democrat, and allowing the removal of those protections is "a serious, serious thing that this body is considering."

"I can think of nothing that is more noxious and nothing that is more damaging," she said.

Rep. Justin Alferman, the Republican from Hermann who sponsored the bill, said it was disingenuous to talk about possible future changes to the voter ID measure that passed Wednesday, because that logic could apply to any bill.

"That's what the Legislature does. We are charged with amending, changing, adding, deleting state statues," he said.

If the measure becomes law, Missouri would join 17 other states that require a photo ID to vote, according to the nonpartisan National Conference of State Legislatures.